1. Field of the Disclosure
The present invention relates generally to power supplies, and more specifically, the present invention relates to power supplies that have capability to operate from a high voltage AC input voltage.
2. Background
In certain applications of AC/DC power supplies, it is sometimes desirable for the power supply to operate outside the normal operating voltage range. Typically, AC/DC power supplies that are designed for worldwide operation are designed to operate with an AC input voltage between 85-265 VAC rms. However, in emerging markets such as India and China, AC input voltages can be as high as 420 VAC for long periods of time under certain conditions.
In the power supply, the AC input voltage is typically rectified by a rectifier circuit to generate a DC voltage, which is applied to the input of a switchmode power converter stage within the power supply. A rectified 420 VAC rms signal generates a peak DC voltage of almost 600V. This high DC voltage greatly increases the cost of the switchmode power converter circuit since all circuitry must be rated for this high voltage condition. In particular, the input capacitors that are normally rated for 400V for an 85-265 VAC rms supply must be increased in voltage rating to at least 600V. This is normally achieved by connecting two 400V capacitors in series across the output terminals of the rectifier circuit. In order to achieve the same effective capacitance in this series arrangement, each capacitor must also be double the capacitance value of the single 400V capacitor they are replacing.
The cost of the power supply circuit is therefore greatly increased in this instance by adding the large additional input capacitors. The space taken by the additional capacitors required is also unacceptable in many applications such as AC/DC power supplies for cell phone charging applications where small enclosures and lightweight are key requirements.